Inline css work but external and internal css doesn't work in index.php

As the question suggests I have an index.php file with html in it and when I try to style it using external or internal css, it doesn't work. But inline css works. By the way I am using xampp on win7 to test the website. And the file structure looks like this c:/xampp/htdocs/test/index.php

<?php
function somefuntion(){
/*I will be adding this function later once the html skeleton
is done.
This function will be calculating some numbers based on the
current date and echoing it.*/
}
?>
</head>